The present invention relates to an electric power steering apparatus which is disposed in a housing rotatably a steering shaft interlocked with a steering wheel and comprises an electric motor for supplying a torque to the steering shaft.
As a power steering apparatus for a vehicle, there has been known, for example, an electric power steering apparatus including in a housing, which houses rotatably a steering shaft interlocked with a steering wheel, an electric motor for supplying a torque to the steering shaft.
In the case where the electric power steering apparatus is of a so-called column assist type, as shown in a depiction of FIG. 1 illustrating a state in which the electric power steering apparatus is mounted on a vehicle body, the electric power steering apparatus comprises a steering shaft 1 connected to a steering wheel 100; a housing 2 for housing the steering shaft 1 rotatably; and a mounting member 3 for mounting the lower side of the housing 2 to a vehicle body 104, and is disposed inside the compartment of the vehicle so that the mounting member 3 is attached to the vehicle body 104 and the center portion of the housing 2 is attached to the vehicle body 104 by a mounting member 4 having an impact force absorber for absorbing an impact force of the secondary collision during a collision.
In this electric power steering apparatus, on the lower side of the housing 2, an electric motor 8 is disposed in the vicinity of the mounting member 3, and a joint 106 for connecting the steering shaft 1 and a steering mechanism to each other is provided to pass through a dash panel 107.
In such an electric power steering apparatus, the steering shaft 1 and housing 2 are respectively divided into a plurality of parts in the axial direction, the divided parts have a structure fitting to each other, and their positional relationship is kept by calking, etc. When an impact force of not less than a predetermined value is applied in an axial direction, the steering shaft 1 and housing 2 shrink as their fitting structures overlap more deeply, and absorb the impact force.
Therefore, in the event of a head-on collision of a vehicle, after the primary collision, when the driver collides with the steering wheel 100 (secondary collision) due to a shock of the primary collision and then the impact force is applied to the steering shaft 1 and housing 2, the steering shaft 1 and housing 2 are pushed in an axial direction and shrink, while the impact force absorber of the mounting member 4 is broken, thereby absorbing the impact force of the secondary collision.
In a conventional electric power steering apparatus as described above, when a head-on collision of a vehicle occurs, if the vehicle body 104 including the dash panel 107 rises due to the impact force of the primary collision, as shown in FIG. 2, a portion of the vehicle body 104 and the mounting member 3, etc. belonging to the vehicle body 104 may be caught on the electric motor 8.
In this case, since the electric motor 8 is fixedly attached to the housing 2, as shown in FIG. 3, the housing 2 and steering shaft 1 can not shrink to an expected degree during the secondary collision, and thus there is a possibility that the impact force of the secondary collision is not sufficiently absorbed.
Moreover, even in the case of an electric power steering apparatus of a so-called pinion assist type, when parts (not shown) such as a transmission (not shown) attached to a vehicle body 104 go down due to the impact force of the primary collision, they may be caught on an electric motor 8. Thus, there is a possibility that the vehicle body 104 can not deform sufficiently and the impact force is not absorbed sufficiently.
For these reasons, positioning of the electric motor 8 poses a problem in installing the electric power steering apparatus on the vehicle body.
An object of the present invention is to provide an electric power steering apparatus capable of solving the above problem.
An electric power steering apparatus according to the first invention, comprising: a housing for housing rotatably a steering shaft interlocked with a steering wheel; an electric motor which has a through hole through which a screw member is to be inserted and is attached to the housing by the screw member through the through hole; and a gear mechanism, connected to the electric motor through a joint, for transmitting a torque of the electric motor to the steering shaft, wherein in order to detach the electric motor from the housing by an impact force in an axial direction of the steering shaft, the through hole has a notch, and the joint is formed by a synthetic resin.
In this electric power steering apparatus according to the first invention, the housing houses rotatably the steering shaft interlocked with the steering wheel; the electric motor has the through hole through which the screw member is to be inserted and is attached to the housing by the screw member through the through hole; and the gear mechanism is connected to the electric motor through the joint and transmits the torque of the electric motor to the steering shaft. The electric motor has the notch in the through hole though which the screw member is to be inserted, and the joint is formed by a synthetic resin. Therefore, when an impact force in an axial direction of the steering shaft is applied, the screw member passes through the notch and comes out of the through hole, while the joint to be an obstacle to the screw member coming out of the through hole is broken, so that the electric motor is detached from the housing.
With this structure, even when a portion of a vehicle body and a mounting bracket, etc. belonging to the vehicle body are caught on the electric motor during the primary collision or secondary collision, since the electric motor is detached from the housing by the impact force of the primary collision or secondary collision, the housing and steering shaft can sufficiently absorb the impact force of the secondary collision, and the position of the electric motor can be easily determined in incorporating it into the vehicle body.
An electric power steering apparatus according to the third invention, comprising: a housing for housing rotatably a steering shaft interlocked with a steering wheel; an electric motor which has a through hole through which a screw member is to be inserted, is positioned by a positioning member and attached to the housing by the screw member through the through hole; and a gear mechanism, connected to the electric motor through a joint, for transmitting a torque of the electric motor to the steering shaft, wherein in order to detach the electric motor from the housing by an impact force in an axial direction of the steering shaft, the through hole has a notch, and the positioning member and joint are formed by a synthetic resin.
In this electric power steering apparatus according to the third invention, the housing houses rotatably the steering shaft interlocked with the steering wheel; the electric motor has the through hole through which the screw member is to be inserted, is positioned by the positioning member and attached to the housing by the screw member through the through hole; and the gear mechanism is connected to the electric motor through the joint and transmits the torque of the electric motor to the steering shaft. The electric motor has the notch in the through hole though which the screw member is to be inserted, and the positioning member and joint are formed by a synthetic resin that is broken more easily than a metal. Therefore, when an impact force in an axial direction of the steering shaft is applied, the screw member passes through the notch and comes out of the through hole, while the positioning member and joint to be obstacles to the screw member coming out of the through hole are broken, so that the electric motor is detached from the housing.
With this structure, even when a portion of a vehicle body and a mounting bracket, etc. belonging to the vehicle body are caught on the electric motor during the primary collision or secondary collision, since the electric motor is detached from the housing by the impact force of the primary collision or secondary collision, the housing and steering shaft can sufficiently absorb the impact force of the secondary collision, and the position of the electric motor can be easily determined in incorporating it into the vehicle body.
The electric power steering apparatus according to the second and fourth inventions, in the first and third inventions, in order to detach the electric motor from the housing by an impact force in an axial direction of the steering shaft, the notch is open from the through hole in an opposite direction to the steering wheel.
The electric power steering apparatus according to the second and fourth inventions, in the first and third inventions, since the notch is open from the through hole in the opposite direction to the steering wheel, even when a portion of a vehicle body and a mounting bracket, etc. belonging to the vehicle body are caught on the electric motor during the primary collision or secondary collision, the electric motor is detached relatively from the housing in the direction of the steering wheel by the impact force of the primary collision or secondary collision. Therefore, the housing and steering shaft can sufficiently absorb the impact force of the secondary collision, and the position of the electric motor can be easily determined in incorporating it into the vehicle body.
An electric power steering apparatus according to the fifth invention, comprising: a housing having at least with two engaging grooves, for housing rotatably a steering shaft interlocked with a steering wheel; an electric motor which has at least two engaging grooves provided at positions corresponding to the at least two grooves of the housing, is positioned by a positioning member and attached to the housing by engaging tightly respective end portions of at least two curved elastic members with the respective at least two engaging grooves of the housing and thereof, and a gear mechanism, connected to the electric motor through a joint, for transmitting a torque of the electric motor to the steering shaft, wherein in order to detach the electric motor from the housing by an impact force in an axial direction of the steering shaft, a part or all of the engaging grooves of the electric motor are open in a predetermined direction, and the positioning member and joint are formed by a synthetic resin.
In this electric power steering apparatus according to the fifth invention, the housing houses rotatably the steering shaft interlocked with the steering wheel and has at least two engaging grooves; and the electric motor has at least two engaging grooves provided at positions corresponding to the at least two grooves of the housing, is positioned by the positioning member and attached to the housing by engaging tightly respective end portions of at least two curved elastic members with the respective two grooves of the housing and thereof. The gear mechanism is connected to the electric motor through the joint and transmits the torque of the electric motor to the steering shaft. A part or all of the engaging grooves of the electric motor are open in a predetermined direction, and the positioning member and joint are formed by a synthetic resin that is more easily broken than a metal. Therefore, when an impact force in an axial direction of the steering shaft is applied, a part or all of the end portions of the elastic members are disengaged in the open direction of the engaging grooves, while the positioning member and joint to be obstacles to the disengagement of the end portions are broken, so that the electric motor is detached from the housing.
With this structure, even when parts such as a transmission attached to a vehicle body go down and are caught on the electric motor during the primary collision, the electric motor is detached from the housing in the opposite direction to the steering wheel by the impact force of the primary collision. Consequently, the vehicle body can deform sufficiently and absorb the impact force of the primary collision sufficiently, and the position of the electric motor can be easily determined in incorporating it into the vehicle body.
An electric power steering apparatus according to the sixth invention, comprising an electric motor attached to a housing for housing rotatably a steering shaft interlocked with a steering wheel, by a screw member through a through hole; and a gear mechanism, connected to the electric motor through a joint, for transmitting a torque of the electric motor to the steering shaft, wherein in order to detach the electric motor from the housing by an impact force in an axial direction of the steering shaft, the screw member and joint are formed by a synthetic resin.
In this electric power steering apparatus according to the sixth invention, the electric motor is attached to the housing for housing rotatably the steering shaft interlocked with the steering wheel, by a screw member through a through hole; and the gear mechanism is connected to the electric motor through the joint and transmits the torque of the electric motor to the steering shaft. Since the screw member and joint are formed by a synthetic resin, when an impact force in an axial direction of the steering shaft is applied, the screw member and joint are broken; and then the electric motor is detached from the housing.
With this structure, even when a portion of a vehicle body and a mounting bracket, etc. belonging to the vehicle body are caught on the electric motor during the primary collision or secondary collision, since the housing and steering shaft can sufficiently absorb the impact force of the primary collision or secondary collision, the position of the electric motor can be easily determined in incorporating it into the vehicle body.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.